JP2021190477A - Iron-based oxide magnetic powder and manufacturing method thereof - Google Patents

Abstract

To provide a manufacturing method of an iron-based oxide magnetic powder composed of ε-iron oxide particles in which a part of Fe sites is replaced with another metal element, in which the number ratio of fine particles is reduced.SOLUTION: There is provided a manufacturing method of an iron-based oxide magnetic powder composed of ε-iron oxide particles in which a part of Fe site is replaced with another metal element. In the method, a raw material slurry containing particles of ε-iron oxide in which a part of Fe site is replaced with another metal element is subjected to hydrothermal treatment.SELECTED DRAWING: Figure 2

Description

The present invention relates to an iron-based oxide magnetic powder suitable for a high-density magnetic recording medium, a radio wave absorber, etc., particularly an iron-based oxide magnetic powder having an average particle diameter of particles on the nanometer order, and a method for producing the same.

ε-Fe ₂ O ₃ is a very rare phase among iron oxide, at room temperature, the particle size of nanometer order is ^{20kOe (1.59 × 10 6 A /} m) of about giant coercive force (Hc ), A production method for synthesizing ε-Fe ₂ O ₃ in a single phase has been studied conventionally (see Patent Document 1).
Further, when ε-Fe ₂ O _{3 is} to be used as a magnetic recording medium, there is no material for a magnetic head having a high level of saturation magnetic flux density corresponding to it at present. Therefore, the coercive force is also adjusted by substituting a part of the Fe site of ε-Fe ₂ O _{3 with} a trivalent metal such as Al, Ga, In, etc., and the coercive force and radio wave absorption are also performed. The relationship between the characteristics has also been investigated (see Patent Document 2).

Since ε-Fe ₂ O ₃ is obtained as a stable phase in a size on the order of nanometers, a special method is required for its production. In the above-mentioned Patent Documents 1 and 2, fine crystals of iron oxyhydroxide produced by the liquid phase method are used as a precursor, and the precursor is coated with a silicon oxide by a sol-gel method and then heat-treated. A method for producing _{Fe 2} O _{3 is disclosed.} As the liquid phase method, a reverse micelle method using an organic solvent as a reaction medium and a method using only an aqueous solution as a reaction medium are disclosed, respectively.

On the other hand, in the field of magnetic recording, a magnetic recording medium having a high ratio of reproduction signal level to particle noise (Carrier to Noise Ratio) is being developed, and magnetism is being developed to increase the recording density. There is a demand for miniaturization of magnetic particles constituting the recording layer. Further, in order to increase the density of magnetic recording, it is also required to reduce the variation in the coercive force distribution due to the presence of fine particles having a small coercive force contained in the iron-based oxide magnetic powder.

Patent Document 3, the slurry containing epsilon-Fe ₂ O ₃ particles or Fe some other metal elements in substituted epsilon-Fe ₂ O ₃ particles of sites, a quaternary ammonium salt as a surface modifier Disclosed is a method for producing an ε-type iron-based oxide magnetic powder, which is added and the pH of the slurry is set to 11 or more and 14 or less, and the ε-iron oxide particles are subjected to a dispersion treatment and then a classification operation is carried out. The document describes that by using the production method, it is possible to obtain a magnetic powder of an ε-type iron-based oxide having a small particle size and a narrow particle size distribution and coercive force distribution.

Japanese Unexamined Patent Publication No. 2008-174405 International Publication No. 2008/029861 Japanese Unexamined Patent Publication No. 2019-175539

The iron-based oxide magnetic powder produced by the production method disclosed in Patent Document 3 and composed of particles of ε-iron oxide in which a part of Fe sites is replaced with other metal elements has a narrow particle size distribution and The content of fine particles that do not contribute to the magnetic recording characteristics was low, and as a result, the coercive force distribution was narrow, which was excellent.
However, according to the studies by the present inventors, there is a quality problem from the viewpoint of increasing the recording density of the magnetic recording medium.

This problem will be specifically described.
When applying an iron-based oxide magnetic powder composed of ε-iron oxide particles to a magnetic recording medium, it is desirable that the particle size is far from the average particle size and the abundance ratio of fine particles is as small as possible. This is because the presence of the fine particles causes an increase in noise in the electromagnetic conversion characteristics (SNR) of the magnetic recording medium even if the volume ratio to the magnetic powder is small.

The iron-based oxide magnetic powder composed of ε-iron oxide particles in which a part of the Fe site produced by the production method disclosed in Patent Document 3 is replaced with another metal element has a fine particle content. It cannot be said that the amount has been sufficiently reduced, and there is a problem from the viewpoint of increasing the recording density of the magnetic recording medium.

The present invention has been made under the above circumstances, and the problem to be solved is ε-oxidation in which the content of fine particles is reduced and a part of Fe sites is replaced with other metal elements. It is an object of the present invention to provide a method for producing an iron-based oxide magnetic powder composed of iron particles. At the same time, it is an object of the present invention to provide an iron-based oxide magnetic powder composed of ε-iron oxide particles in which a part of Fe sites is replaced with other metal elements, in which the content of fine particles is reduced.

As a result of diligent research by the present inventors in order to solve the above-mentioned problems, hydrothermal treatment is performed on a slurry containing ε-iron oxide particles in which a part of Fe sites containing fine particles is replaced with other metal elements. The present invention was completed with the epoch-making finding that the content of the fine particles can be reduced by applying the above.

That is, the first invention for solving the above-mentioned problems is
A raw material slurry containing particles of ε-iron oxide in which a part of Fe sites is substituted with other metal elements is subjected to hydrothermal treatment, and ε-oxidation in which a part of Fe sites is substituted with other metal elements. This is a method for producing an iron-based oxide magnetic powder composed of iron particles.
The second invention is
By the hydrothermal treatment, the number ratio of ε-iron oxide particles in which a part of the Fe site is replaced with another metal element and the particle size measured by a transmission electron microscope is 8 nm or less is reduced. The method for producing iron-based oxide magnetic powder according to the first invention, which comprises the above.
The third invention is
The method for producing an iron-based oxide magnetic powder according to a second invention, which comprises reducing the number ratio of particles having a particle diameter of 8 nm or less as measured by the transmission electron microscope to 4% or less. ..
The fourth invention is
The method for producing an iron-based oxide magnetic powder according to any one of the first to third inventions, which comprises performing the hydrothermal treatment at a temperature of 120 ° C. or higher.
The fifth invention is
The method for producing an iron-based oxide magnetic powder according to any one of the first to fourth inventions, which comprises performing the hydrothermal treatment at a pressure of 0.2 MPa or more.
The sixth invention is
The production of the iron-based oxide magnetic powder according to any one of the first to fifth inventions, wherein the raw material slurry containing the particles of ε-iron oxide has a pH of 6 or more and 14 or less. The method.
The seventh invention is
The raw material slurry containing the ε-iron oxide particles contains ε-iron oxide particles having an average particle diameter of 10 nm or more and 20 nm or less as measured by a transmission electron microscope, in which a part of Fe sites is replaced with other metal elements. The method for producing an iron-based oxide magnetic powder according to any one of the first to sixth inventions, which comprises using a slurry.
The eighth invention is
The method for producing an iron-based oxide magnetic powder according to any one of the first to seventh inventions, which comprises using Ga as another metal element that replaces a part of the Fe site.
The ninth invention is
The iron according to any one of the first to eighth inventions, which comprises subjecting the raw material slurry containing ε-iron oxide particles to ultrasonic heat treatment after irradiating ultrasonic waves and / or adding metal ions. This is a method for producing an oxide magnetic powder.
The tenth invention is
The average particle size measured by a transmission electron microscope is 10 nm or more and 20 nm or less, the number ratio of particles having a particle size of 8 nm or less is 4% or less, and the α-type iron-based oxide measured by the X-ray diffractometry. It is an iron-based oxide magnetic powder composed of ε-iron oxide particles in which a part of Fe sites is substituted with other metal elements, which is characterized by a content of 10% or less.
The eleventh invention is
The iron-based oxide magnetic powder according to the tenth invention, wherein the other metal element that replaces a part of the Fe site is Ga.

Ε Iron oxide particles having a reduced content of fine particles by a method for producing an iron-based oxide magnetic powder composed of ε-iron oxide particles in which a part of Fe sites according to the present invention is substituted with other metal elements. An iron-based oxide magnetic powder made of the above can be obtained.

It is a TEM photograph of the substitution type ε iron oxide particle which concerns on Example 1. FIG. It is a TEM photograph of the iron-based oxide magnetic powder which concerns on Example 1. FIG. It is a TEM photograph of the iron-based oxide magnetic powder which concerns on Example 4. FIG. It is a TEM photograph of the iron-based oxide magnetic powder which concerns on Example 7. FIG. It is a TEM photograph of the substitution type ε iron oxide particle which concerns on Example 10. FIG. It is a TEM photograph of the iron-based oxide magnetic powder which concerns on Example 10.

In the method for producing an iron-based oxide magnetic powder composed of ε-iron oxide particles in which a part of Fe site is replaced with another metal element according to the present invention, a part of Fe site is replaced with another metal element. It is characterized in that a slurry containing particles of ε-iron oxide (may be referred to as “raw material slurry” in the present invention) is subjected to hydrothermal treatment. The hydrothermal treatment is preferably performed at a temperature of 120 ° C. or higher, preferably at a pressure of 0.2 MPa or higher, preferably a raw material slurry having a pH of 6 or more and 14 or less, and permeated as a raw material slurry. It is preferable to use a slurry having an average particle diameter of 10 nm or more and 20 nm or less measured by an electron microscope and containing ε-iron oxide particles in which a part of Fe sites is replaced with another metal element, and ultrasonic waves are used as the raw material slurry. It is preferable to subject the particles to hydrothermal treatment after irradiation.
Further, the present invention is an iron-based oxide magnetic powder composed of ε-iron oxide particles in which a part of Fe sites is replaced with other metal elements, and the average particle diameter measured by a transmission electron microscope is 10 nm or more and 20 nm or less. The ratio of the number of fine particles having a particle size of 8 nm or less to the predetermined number of particles of the substituted iron oxide (in the present invention, the ratio of the number of fine particles to the predetermined number of particles of the substituted iron oxide) is simply used. It may be described as "number ratio"), preferably 4% or less, and the content of α-type iron oxide measured by the X-ray diffractometry is 10% or less. Related to things. The metal element that replaces a part of the Fe site may be Ga.

Hereinafter, the present invention will be described in detail in the order of [method for producing iron-based oxide magnetic powder] and [iron-based oxide magnetic powder]. "Ε iron oxide" may be described as "replacement type ε iron oxide", and "particles of ε iron oxide in which a part of Fe site is replaced with another metal element" may be described as "replacement type ε iron oxide particles". ..

[Manufacturing method of iron-based oxide magnetic powder]
Regarding the method for producing an iron-based oxide magnetic powder according to the present invention, 1. Manufacture of raw material slurry, 2. Pretreatment to raw material slurry, 3. Hydrothermal treatment of the raw material slurry will be described in detail in this order.

1. 1. Production of Raw Material Slurry First, as a raw material slurry, a slurry containing substituted ε-iron oxide particles is prepared. Here, since the raw material slurry contains the substituted ε-iron oxide particles, the substituted ε-iron oxide particles according to the present invention can be obtained after the hydrothermal treatment described later.

As a method for preparing the substituted ε-iron oxide particles, a known production method for iron-based oxide magnetic powder composed of ε-iron oxide particles can be used. Examples of the known production method include Japanese Patent Application Laid-Open No. 2019-175539 and Japanese Patent Application Laid-Open No. 2017-024981.

A raw material slurry can be obtained by mixing the substituted ε-iron oxide particles obtained by the above-mentioned known production method with a solvent. Here, the solvent is preferably water.
As described in the paragraph of the silicon oxide coating removing step (0041) of JP-A-2017-024981, a slurry containing substituted ε-iron oxide particles coated with silicon oxide is contained in a strong alkaline aqueous solution. The silicon oxide is dissolved and removed from the substituted iron oxide particles by immersing in and stirring the iron oxide particles. After that, the substituted iron oxide particles cannot pass through the ultrafiltration membrane, etc., and the unnecessary ions constituting the dissolved silicon oxide and the strong alkali can pass through the ultrafiltration membrane, etc., and are substituted type. The raw material slurry may be obtained by washing the slurry containing the ε-iron oxide particles with water to remove the dissolved substances of the silicon oxide and unnecessary ions.

The composition and particle size of the substituted ε-iron oxide particles contained in the raw material slurry are not particularly limited, and may be adjusted according to the composition and particle size of the iron-based oxide magnetic powder to be finally obtained. Further, the concentration of the substituted ε-iron oxide particles in the raw material slurry is not particularly limited, and may be usually about 0.1 to 10% by mass.

Here, the composition of the substituted ε-iron oxide particles to which the production method of the present invention can be applied will be described.
(1) A general formula ε-C _z Fe _2-z O ₃ (where C is one or more trivalent metal elements selected from In, Ga, and Al).
(2) In formula _{ε-A x B y Fe 2} -xy O 3 ( where A is, Co, Ni, Mn, 1 or more divalent metal element selected from Zn, B is Ti, and Sn One or more selected tetravalent metal elements).
(3) General formula ε-A _x C _z Fe _2-xz O ₃ (where A is one or more divalent metal elements selected from Co, Ni, Mn and Zn, and C is In and Ga. , One or more trivalent metal elements selected from Al).
(4) General formula ε-B _y C _z Fe _2-yz O ₃ (where B is one or more tetravalent metal elements selected from Ti and Sn, and C is selected from In, Ga and Al. It is represented by one or more trivalent metal elements).
(5) the general formula _{ε-A x B y C z} Fe 2-xyz O 3 ( where A, Co, Ni, Mn, 1 or more divalent metal element selected from Zn, B is, Ti , One or more tetravalent metal elements selected from Sn, C is one or more trivalent metal elements selected from In, Ga, Al).

The substitution amounts x, y and z in each of the general formulas described in (1) to (5) above are arbitrary quantities in the range of 0 <x <1, 0 <y <1, 0 <z <1. can do. Then, the coercive force can be adjusted to a desired value by adjusting the substitution amounts x, y and z.

The iron-based oxide magnetic powder composed of substituted ε-iron oxide particles produced by the method for producing iron-based oxide magnetic powder according to the present invention contains different phases, which are impurities that are inevitably produced in the production thereof. In some cases. The heterogeneous phase is mainly α-type iron-based oxides. In the iron-based oxide magnetic powder composed of substituted ε-iron oxide particles obtained by the production method according to the present invention, the content of α-type iron-based oxide is permitted, but the content thereof is suppressed. Is preferable. Note that the alpha-type iron-based oxide, in alpha-Fe ₂ portion of O ₃ and Fe site is a generic term for have been alpha-Fe ₂ O ₃ replaced by another metal element (present invention, alpha type The iron-based oxide of is sometimes referred to as "α phase").

The pH of the raw material slurry is preferably 6 or more and 14 or less from the viewpoint of suppressing an increase in the α phase content in the iron-based oxide magnetic powder obtained after the hydrothermal treatment described later.
By setting the pH of the raw material slurry to 6 or more, the α phase content of the obtained iron-based oxide magnetic powder can be suppressed. Further, by setting the pH of the raw material slurry to 14 or less, it is possible to prevent the effect of suppressing the increase in the α phase content from reaching a plateau, and it is possible to avoid an increase in the chemical cost of the alkaline agent, which is preferable.

If a raw material slurry having a desired pH range cannot be obtained, the pH may be adjusted to a desired range and used as the raw material slurry by adding an acid, an alkali or the like to the slurry. Inorganic acids such as sulfuric acid, nitric acid, hydrochloric acid and acetic acid can be used as the acid to be added, and alkali metal hydroxides such as sodium hydroxide and alkaline earth metals such as calcium hydroxide can be added as alkalis. Inorganic alkalis such as hydroxides and ammonia can be used.

In the present invention, the pH value is measured using a glass electrode based on JIS Z8802, and is measured by a pH meter calibrated using an appropriate buffer solution according to the pH range to be measured as a pH standard solution. It was done. Further, the pH described in the present invention is a value obtained by directly reading the measured value indicated by the pH meter compensated by the temperature compensating electrode under the reaction temperature condition.

2. 2. Pretreatment of raw material slurry The raw material slurry prepared in "1. Production of raw material slurry" may be treated as "pretreatment post-treatment slurry" by performing pretreatment such as ultrasonic irradiation and / or addition of metal ions. This is a preferred configuration.

Ultrasonic irradiation of the raw material slurry can be carried out by a known ultrasonic disperser. By performing the hydrothermal treatment after irradiating the raw material slurry with ultrasonic waves, the content of fine particles in the obtained iron-based oxide magnetic powder can be further reduced as compared with the case where the raw material slurry is not irradiated with ultrasonic waves.

The addition of metal ions to the raw material slurry can be carried out by adding a water-soluble metal salt such as ferric nitrate or gallium nitrate to the raw material slurry.
However, the type of metal element of the water-soluble metal salt to be added and the addition ratio of each element may be adjusted to the chemical composition of the substituted ε iron oxide particles contained in the raw material slurry, but the substituted type contained in the raw material slurry may be used. The type of metal element and each element within the range of the substitution amount in each general formula described in (1) to (5) of "1. Production of raw material slurry" above, regardless of the chemical composition of the ε iron oxide particles. The addition ratio may be set. Further, only a water-soluble iron salt such as ferric sulfate may be added without adding the substituted metal element. Here, the amount of metal ions added is preferably such that the total concentration of metal ions in the raw material slurry is 0.1 mol / kg or less. And it is preferable to contain ^{Fe 3+} ions as iron ions. Further, as the anion species of the water-soluble metal salt to be added, an anion species contained in an inorganic acid such as sulfate ion, nitrate ion, chloride ion and acetate ion can be used.

3. 3. Hydrothermal treatment of raw material slurry Hydrothermal treatment is a process of holding an object to be treated in hot water at a high temperature of more than 100 ° C. and high pressure.
By carrying out hydrothermal treatment in the production method according to the present invention, it is possible to reduce the number ratio of fine particles of substituted ε-iron oxide contained in the raw material slurry or the raw material slurry after the pretreatment. The reason why the number ratio of the fine particles can be reduced is not clear, but the inventors have estimated the following mechanism.

Exposure of the substituted iron oxide particles to hot water at high temperature and high pressure causes a dissolution-reprecipitation reaction of the substituted iron oxide particles. By this dissolution reprecipitation reaction, the fine particles of the substituted iron oxide in the raw material slurry are dissolved and reprecipitated around the substituted ε iron oxide particles having a larger particle size. It is considered that the content of fine particles is reduced by the above mechanism. Such a phenomenon of dissolution and reprecipitation is generally known as Ostwald ripening.
Hereinafter, specific aspects such as temperature, pressure, and time of the hydrothermal treatment according to the present invention will be described.

The temperature of the hydrothermal treatment is preferably 120 ° C. or higher, more preferably 170 ° C. or higher, in order to obtain the effect of reducing the number ratio of fine particles of substituted ε-iron oxide, which is the object of the present invention. Further, when a raw material slurry having a large number ratio of fine particles such as 20% or more of particles having a particle diameter of 8 nm or less is used, water is used from the viewpoint of ensuring a sufficient effect of reducing the number ratio of fine particles. The heat treatment temperature is preferably 280 ° C. or higher.
On the other hand, from the viewpoint of suppressing the number ratio of α phase in the obtained iron-based oxide magnetic powder, the temperature is preferably 450 ° C. or lower, and more preferably 380 ° C. or lower.
The pressure of the hydrothermal treatment is preferably 0.2 MPa or more, and more preferably 10 MPa or more, in order to obtain the effect of reducing the number ratio of fine particles of the substituted iron oxide, which is the object of the present invention. On the other hand, the upper limit of the hydrothermal treatment pressure is not particularly limited, but the pressure may be 600 MPa or less, or 100 MPa or less, from the viewpoint of equipment cost.
The time of the hydrothermal treatment is preferably 1 minute or more in order to obtain the effect of reducing the number ratio of fine particles of substituted ε-iron oxide, which is the object of the present invention. On the other hand, the upper limit of the hydrothermal treatment time is not particularly limited, but from the viewpoint of production cost, the time may be 600 minutes or less, or 100 minutes or less.
By the above operation, the ratio of the number of fine particles was reduced by the method for producing an iron-based oxide magnetic powder composed of ε-iron oxide particles in which a part of Fe sites according to the present invention was replaced with other metal elements. An iron-based oxide magnetic powder composed of ε-iron oxide particles could be obtained without performing a classification operation.
However, if desired, it is a preferable configuration to carry out a preliminary classification operation before the hydrothermal treatment. Further, if desired, it is also preferable to repeat the hydrothermal treatment a plurality of times.

[Iron-based oxide magnetic powder]
By the above-described method for producing an iron-based oxide magnetic powder according to the present invention, the raw material slurry or the raw material slurry after pretreatment is subjected to the above-mentioned hydrothermal treatment, whereby the number ratio of fine particles is reduced. A slurry containing ε iron oxide particles is obtained. By solid-liquid separation of the obtained slurry by a known method, recovery of the solid content, and then drying, an iron-based oxide magnetic powder having a reduced number ratio of fine particles can be obtained.
Regarding the aspect of the iron-based oxide magnetic powder obtained by the production method according to the present invention, 1. TEM particle size, 2. Crystal structure, 3. α phase content, 4. The composition will be described in detail in this order.

1. 1. TEM particle size In the post-process described later, when iron-based oxide magnetic powder for magnetic recording media is produced, the coercive force of the obtained iron-based oxide magnetic powder is increased to some extent, and excellent electromagnetic conversion of the magnetic recording medium is performed. In order to obtain the characteristics, the substituted iron oxide particles constituting the iron-based oxide magnetic powder according to the present invention have an average particle size measured by a transmission electron microscope (when described as "TEM average particle size" in the present invention. ) Is preferably 10 nm or more and 20 nm or less.
In the present invention, the particle size refers to the particle size of the smallest unit of particles (primary particles) whose contour is observed with a transmission electron microscope.

As described above, if the average particle size of the substituted iron oxide particles measured by the transmission electron microscope becomes too small, the abundance ratio of fine particles that do not contribute to the improvement of magnetic characteristics increases, and the magnetic characteristics per unit weight of the magnetic powder. Deteriorates. Therefore, the TEM average particle size is preferably 10 nm or more.
On the other hand, when the TEM average particle size is 20 nm or less, more preferably 18 nm or less, the electromagnetic conversion characteristics when the iron-based oxide magnetic powder is used as a magnetic recording medium can be improved.

In the iron-based oxide magnetic powder according to the present invention, the ratio of the number of fine particles of substituted ε-iron oxide having a TEM particle size of 8 nm or less to a predetermined number of particles of substituted ε-iron oxide is 4% or less. preferable. This is because the fine particles of substituted ε-iron oxide having a TEM particle diameter of 8 nm or less have a low coercive force, so that they cannot be magnetically recorded even if they exist in a magnetic recording medium. This is because the particles can lead to an increase in the noise component in the electromagnetic conversion characteristics.
The predetermined number of particles of the above-mentioned substituted ε-iron oxide is 200 or more.

Therefore, it is preferable that the ratio of the number of fine particles of the substituted ε-iron oxide having a TEM particle diameter of 8 nm or less to the predetermined number of particles of the substituted ε-iron oxide is as small as possible. In the iron-based oxide magnetic powder according to the present invention, the number ratio of fine particles of substituted ε-iron oxide having a TEM particle size of 8 nm or less is preferably 4% or less. This is because the amount of noise component in the electromagnetic conversion characteristics when the iron-based oxide magnetic powder is used as a magnetic recording medium can be reduced as compared with the case where the conventional iron-based oxide magnetic powder is used. ..

2. 2. Crystal structure It can be confirmed by using X-ray diffraction method (XRD), high-speed electron diffraction method (HEED), etc. that the iron-based oxide magnetic powder according to the present invention has a crystal structure of ε-iron oxide. I can.

3. 3. α-phase content As described above, the iron-based oxide magnetic powder obtained by the production method of the present invention may contain an α-phase. When applying the iron-based oxide magnetic powder according to the present invention to a magnetic recording medium, it is preferable to reduce the content ratio of the heterogeneous phase in the iron-based oxide magnetic powder as much as possible. Specifically, when the content ratio of the heterogeneous phase in the iron-based oxide magnetic powder is measured by Rietveld analysis by the X-ray diffraction method, the content ratio of the α phase is preferably 10% or less.

4. Composition The composition of the iron-based oxide magnetic powder according to the present invention is the same as that of the substituted iron oxide prepared as a raw material when the metal ion is not added as a pretreatment for the hydrothermal treatment.
On the other hand, when metal ions are added as a pretreatment for hydrothermal treatment, all the added metal ions are taken into the iron-based oxide particles as oxides, so that the iron-based oxide magnetic powder finally obtained The composition is a combination of the substituted iron oxide prepared as a raw material and the added metal ion.

Hereinafter, the present invention will be specifically described with reference to Examples. The present invention is not limited to the embodiment.
First, regarding the evaluation method and evaluation apparatus for the substituted ε-iron oxide particles obtained by the production method according to the present invention and the iron-based oxide magnetic powder composed of the substituted ε-iron oxide particles, 1. TEM measurement, 2. Average particle size, particle size distribution measurement, 3. Crystallinity evaluation by X-ray diffraction method (XRD), 4. 3. Magnetic hysteresis curve (BH curve) measurement. Chemical composition analysis will be explained in this order.

1. 1. TEM observation JEM-1011 manufactured by JEOL Ltd. was used for TEM observation. For the observation of the substituted ε-iron oxide particles, a TEM photograph taken at a magnification of 100,000 times was used (the one after removing the silicon oxide coating was used).

2. 2. Measurement of average particle size and particle size distribution Digitization was used to evaluate the TEM average particle size and particle size distribution of the substituted iron oxide particles. Mac-View Ver.4.0 was used as the image processing software. When this image processing software is used, the particle size of a certain particle is calculated as the length of the long side of the rectangle having the smallest area among the rectangles circumscribing the particle. As for the number, 200 pieces were measured.

At this time, among the particles shown in the TEM photograph, the selection criteria of the particles to be measured were as follows.
(1) Particles in which a part of the particles protrudes out of the field of view of the photograph are not measured.
(2) Particles that have a clear outline and exist in isolation are measured.
(3) Even if the particle shape deviates from the average particle shape, the particles that are independent and can be measured as single particles are measured.
(4) For particles in which the particles overlap each other, but the boundary between the two is clear and the shape of the entire particle can be determined, each particle is measured as a single particle.
(5) Particles that overlap and whose boundaries are not clear and whose overall shape is unknown are not measured as the shape of the particles cannot be determined.
The average number of particle sizes of the particles selected according to the above criteria (1) to (5) was calculated and used as the average particle size by TEM observation of the iron oxide magnetic powder. Further, the value obtained by dividing the "standard deviation of the particle size of the selected particles" by the "number average value (= average particle size) of the particle size of the selected particles" is calculated, and the TEM of the iron oxide magnetic powder is calculated. The coefficient of variation of the particle size by observation was used. Further, the ratio of the number of particles having a particle diameter of 8 nm or less to the number of selected particles is calculated as a percentage to obtain a particle ratio of 8 nm or less, and the particle diameter of the selected particles is 20 nm. The number ratio of the above particles was calculated as a percentage to obtain a particle ratio of 20 nm or more.

3. 3. Crystalline evaluation by X-ray diffraction method (XRD) Powder X-ray diffraction (XRD: Rigaku sample horizontal multipurpose X-ray diffractometer Ultima IV, source CuKα ray, voltage 40 kV, current 40 mA, 2θ = 10 ° or more and 70 ° or less). The obtained diffraction pattern was based on ICSD (Inorganic Crystal Structure Database) No. 173025: Iron (III) Oxide-Epsilon, No. 82134: Hematite using integrated powder X-ray analysis software (PDXL2: manufactured by Rigaku Co., Ltd.). The crystal structure and α-phase content were confirmed by evaluation by Rietveld analysis.

4. Magnetic Hysteresis Curve (BH Curve) Measurement The magnetic properties of the obtained iron-based oxide magnetic powder were measured under the following conditions.
A vibrating sample magnetometer (VSM) (VSM-5 manufactured by Toei Kogyo Co., Ltd.) is used as a magnetic characteristic measuring device, and the applied magnetic field is 1035 kA / m (13 kOe), M measurement range is 0.005 A ・ m ² (5 emu), and the applied magnetic field. The magnetic characteristics were measured at a change rate of 15 (kA / m · s), a time constant of 0.03 seconds, and a weight time of 0.1 seconds. In addition, the attached software (Ver.2.1) manufactured by Toei Kogyo Co., Ltd. was used for this measurement.

5. Chemical composition analysis In the chemical composition analysis of the iron-based oxide magnetic powder, ICP-720ES manufactured by Azilent Technology was used, and the measurement wavelength (nm) was Fe; 259.940 nm and Ga; 294.363 nm. ..

[Example 1]
(Procedure 1)
As a raw material solution, 3000 g of a mixed aqueous solution of ferric nitrate (III) and gallium nitrate was prepared. In this raw material solution, the molar ratio of Fe ion to Ga ion was 1.55: 0.45, and the total molar concentration of Fe ion and Ga ion was 0.50 mol / kg.
Under an air atmosphere, the raw material solution was set to 40 ° C., and 275.6 g of a 21.75% aqueous ammonia solution was added all at once while mechanically stirring with a stirring blade, and stirring was continued for 2 hours.
Next, under the condition of a solution temperature of 40 ° C., 288.8 g of a citric acid solution having a citric acid concentration of 20% by mass was continuously added over 1 hour, and then 186.1 g of a 21.75% by mass aqueous ammonia solution was added all at once. did. Then, stirring was maintained for 1 hour under the condition of a solution temperature of 40 ° C. to produce a slurry containing iron oxyhydroxide crystals containing Ga as a substituent.

(Procedure 2)
Then, under an atmospheric atmosphere, 833.7 g of tetraethoxysilane (TEOS) was added over 35 minutes while stirring the slurry obtained in step 1 at 40 ° C. Then, stirring was continued as it was for about 1 day to obtain a slurry in which crystals of iron oxyhydroxide containing a substituent were coated with a hydrolysis product of TEOS. Then, the obtained slurry was separated into solid and liquid, and the separated solid content was washed and recovered as a cake.

(Procedure 3)
After the cake recovered in step 2 is dried to obtain dry powder, the dry powder is heat-treated at 1025 ° C. for 4 hours in a furnace in an air atmosphere, and substituted ε-oxidation coated with silicon oxide. A powder composed of iron particles was obtained.

(Procedure 4)
The powder composed of the substituted iron oxide particles coated with the silicon oxide obtained in step 3 is added to a 20 mass% NaOH aqueous solution and stirred at about 60 ° C. for 24 hours to prepare the surface of the substituted iron oxide particles. By removing the silicon oxide, a slurry containing substituted ε-iron oxide particles was obtained.

(Procedure 5)
The slurry obtained in step 4 was washed with pure water until the conductivity of the filtrate became ≦ 10 mS / m using an ultrafiltration membrane to obtain a raw material slurry containing substituted ε-iron oxide particles. .. The raw material slurry obtained at this time contained 1% by mass of substituted ε-iron oxide particles. The pH of the obtained raw material slurry was 9.

TEM observation was performed on the raw material slurry obtained in the above procedure 5, and the particle size of 200 particles contained in the slurry was measured. The TEM average particle size was 11.3 nm and the particle size was 8 nm or less. The number ratio of the particles was 23.0%, and the coefficient of variation (CV value) was 36%. The TEM observation of the raw material slurry means that the raw material slurry is dropped and adhered to a collodion film on the grid, naturally dried, and then carbon-deposited to be subjected to TEM observation. FIG. 1 shows a TEM photograph of substituted ε-iron oxide particles contained in the slurry. The length indicated by the white horizontal line displayed at the lower right of the TEM photograph is 100 nm (the same applies to the following TEM photographs).

A 1% by mass aqueous sulfuric acid solution was added to the raw material slurry obtained in step 5 to adjust the pH to 6.5 to aggregate the substituted iron oxide particles, and then filtered through a membrane filter (pore size 0.2 μm). And the solid content was recovered. The recovered solid content was dried to obtain an iron-based oxide magnetic powder composed of substituted ε-iron oxide particles. When the composition analysis of Fe and Ga was carried out on the obtained iron-based oxide magnetic powder, it was found that Fe: Ga = 1.57: 0.43 in terms of molar ratio. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 0%.

(Procedure 6)
The replacement type ε according to Example 1 was placed in a closed container having a capacity of 5 mL and subjected to hydrothermal treatment under the conditions of a treatment temperature of 150 ° C., a treatment time of 5 minutes, and a pressure of 30 MPa. A slurry containing iron oxide particles was obtained.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above.

(Procedure 7)
When TEM observation was performed on the slurry obtained in step 6 and the particle diameters of 200 particles contained in the slurry were measured, the TEM average particle diameter was 11.4 nm and the number of particles having a particle diameter of 8 nm or less. The ratio was 17.4% and the coefficient of variation (CV value) was 33%. FIG. 2 shows a TEM photograph of the substituted ε iron oxide particles according to Example 1.
Next, 1% by mass of a sulfuric acid aqueous solution was added to the slurry obtained in step 6 to adjust the pH to 6.5, filtered through a membrane filter (pore size 0.2 μm), and dried after recovering the solid matter. The iron-based oxide magnetic powder according to Example 1 was obtained.
The obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 0%.
The results of measuring the magnetic properties of the obtained iron-based oxide magnetic powder are shown in the table together with the measurement results of the α phase content and the chemical composition. The chemical composition of the iron-based oxide magnetic powder was equivalent to that of the substituted ε-iron oxide particles contained in the raw material slurry according to Example 1. (The same applies to the following Examples 2 to 10)
Table 2 shows the measurement results of the substituted ε-iron oxide particles and the iron-based oxide magnetic powder described above.

[Example 2]
In step 6 of Example 1, 4.4 mL of the slurry containing the substituted ε-iron oxide particles obtained in Step 5 of Example 1 was used as the raw material slurry, and hydrothermal treatment was performed under the condition of a treatment temperature of 200 ° C. Obtained an iron-based oxide magnetic powder composed of a slurry containing substituted ε-iron oxide particles according to Example 2 and a substituted ε-iron oxide particles according to Example 2 by the same procedure as in Example 1.
As described in step 7 of Example 1, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Example 2, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 12.7 nm, the number ratio of particles having a particle diameter of 8 nm or less was 12.0%, and the coefficient of variation (CV value) was 32%. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 0%.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder.

[Example 3]
In step 6 of Example 1, 4.1 mL of the slurry containing the substituted ε-iron oxide particles obtained in Step 5 of Example 1 was used as the raw material slurry, and hydrothermal treatment was performed under the condition of a treatment temperature of 250 ° C. Obtained an iron-based oxide magnetic powder composed of a slurry containing substituted ε-iron oxide particles according to Example 3 and a substituted ε-iron oxide particles according to Example 3 by the same procedure as in Example 1.
As described in step 7 of Example 1, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Example 3, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 11.9 nm, the number ratio of particles having a particle diameter of 8 nm or less was 13.8%, and the coefficient of variation (CV value) was 28%. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 0%.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder.

[Example 4]
In step 6 of Example 1, 3.8 mL of the slurry containing the substituted ε-iron oxide particles obtained in Step 5 of Example 1 was used as the raw material slurry, and hydrothermal treatment was performed under the condition of a treatment temperature of 300 ° C. Obtained an iron-based oxide magnetic powder composed of a slurry containing substituted ε-iron oxide particles according to Example 4 and particles of substituted ε-iron oxide according to Example 4 by the same procedure as in Example 1. ..
As described in step 7 of Example 1, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Example 4, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 13.1 nm, the number ratio of particles having a particle diameter of 8 nm or less was 4.2%, and the coefficient of variation (CV value) was 30%. FIG. 3 shows a TEM photograph of the iron-based oxide magnetic powder obtained in this example. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 3%.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder.

[Example 5]
In step 6 of Example 1, 3.2 mL of the slurry containing the substituted ε-iron oxide particles obtained in Step 5 of Example 1 was used as the raw material slurry, and hydrothermal treatment was performed under the condition of a treatment temperature of 350 ° C. Obtained an iron-based oxide magnetic powder composed of a slurry containing substituted ε-iron oxide particles according to Example 5 and particles of substituted ε-iron oxide according to Example 5 by the same procedure as in Example 1. ..
As described in step 7 of Example 1, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Example 5, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 14.2 nm, the number ratio of particles having a particle diameter of 8 nm or less was 0.4%, and the coefficient of variation (CV value) was 28%. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 5%.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder.

[Example 6]
In step 6 of Example 1, 3.2 mL of the slurry containing the substituted ε-iron oxide particles obtained in Step 5 of Example 1 was used as the raw material slurry, and water was used under the conditions of a treatment temperature of 350 ° C. and a treatment time of 10 minutes. An iron-based oxide composed of a slurry containing substituted ε-iron oxide particles according to Example 6 and particles of substituted ε-iron oxide according to Example 6 according to the same procedure as in Example 1 except that the heat treatment was performed. A magnetic powder was obtained.
As described in step 7 of Example 1, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Example 6, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 15.4 nm, the number ratio of particles having a particle diameter of 8 nm or less was 0.4%, and the coefficient of variation (CV value) was 45%. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 7%.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder.

[Example 7]
In step 6 of Example 1, 3.2 mL of the slurry containing the substituted ε-iron oxide particles obtained in Step 5 of Example 1 was used as the raw material slurry, and water was used under the conditions of a treatment temperature of 350 ° C. and a treatment time of 30 minutes. An iron-based oxide composed of a slurry containing substituted ε-iron oxide particles according to Example 7 and particles of substituted ε-iron oxide according to Example 7 according to the same procedure as in Example 1 except that the heat treatment was performed. A magnetic powder was obtained.
As described in step 7 of Example 1, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Example 7, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 15.1 nm, the number ratio of particles having a particle diameter of 8 nm or less was 0.6%, and the coefficient of variation (CV value) was 36%. FIG. 4 shows a TEM photograph of the iron-based oxide magnetic powder obtained in Example 7. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 8%.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder.

[Example 8]
In step 6 of Example 1, 3.2 mL of the slurry containing the substituted ε-iron oxide particles obtained in Step 5 of Example 1 was used as the raw material slurry, and water was used under the conditions of a treatment temperature of 350 ° C. and a treatment time of 60 minutes. An iron-based oxide composed of a slurry containing substituted ε-iron oxide particles according to Example 8 and particles of substituted ε-iron oxide according to Example 8 according to the same procedure as in Example 1 except that the heat treatment was performed. A magnetic powder was obtained.
As described in step 7 of Example 1, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Example 8, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 15.4 nm, the number ratio of particles having a particle diameter of 8 nm or less was 0.6%, and the coefficient of variation (CV value) was 36%. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 12%.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder.

[Example 9]
In step 6 of Example 1, 3.2 mL of the slurry containing the substituted ε-iron oxide particles obtained in Step 5 of Example 1 was used as the raw material slurry, and water was used under the conditions of a treatment temperature of 400 ° C. and a treatment time of 5 minutes. An iron-based oxide composed of a slurry containing substituted ε-iron oxide particles according to Example 9 and particles of substituted ε-iron oxide according to Example 9 according to the same procedure as in Example 1 except that the heat treatment was performed. A magnetic powder was obtained.
As described in step 7 of Example 1, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Example 9, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 16.0 nm, the number ratio of particles having a particle diameter of 8 nm or less was 0.0%, and the coefficient of variation (CV value) was 36%. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 14%.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder.

[Comparative Example 1]
Comparative Example according to the same procedure as in Example 1 except that the slurry containing the substituted ε-iron oxide particles obtained in the procedure 5 of Example 1 was not subjected to hydrothermal treatment in the procedure 6 of the first embodiment. An iron-based oxide magnetic powder composed of a slurry containing substituted ε-iron oxide particles according to No. 1 and particles of substituted ε-iron oxide according to Comparative Example 1 was obtained.
As described in step 7 of Example 1, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Comparative Example 1, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 11.3 nm, the number ratio of particles having a particle diameter of 8 nm or less was 23.0%, and the coefficient of variation (CV value) was 36%. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 0%.
Table 1 shows the processing conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder.

[Example 10]
(Procedure 1)
As a raw material solution, 6000 g of a mixed aqueous solution of ferric chloride (III) and gallium nitrate was prepared. In the raw material solution, the molar ratio of Fe ion to Ga ion was 1.90: 0.10, and the total molar concentration of Fe ion and Ga ion was 0.50 mol / kg.
In the air atmosphere, the raw material solution was set to 40 ° C., and 546.1 g of a 22.46% aqueous ammonia solution was added all at once while mechanically stirring with a stirring blade, and stirring was continued for 2 hours.
Next, under the condition of a solution temperature of 40 ° C., 577.5 g of a citric acid aqueous solution having a citric acid concentration of 20% by mass was continuously added over 1 hour, and then 368.7 g of a 22.46% by mass aqueous ammonia solution was added all at once. did. Then, stirring was maintained for 1 hour under the condition of a solution temperature of 40 ° C. to produce a slurry containing iron oxyhydroxide crystals containing Ga as a substituent.

(Procedure 2)
Then, in the air atmosphere, 1692.7 g of tetraethoxysilane (TEOS) was added over 35 minutes while stirring the slurry obtained in step 1 at 40 ° C. Then, stirring was continued as it was for about 1 day to obtain a slurry in which crystals of iron oxyhydroxide containing a substituent were coated with a hydrolysis product of TEOS. Then, the obtained slurry was separated into solid and liquid, and the separated solid content was washed and recovered as a cake.

(Procedure 3)
After the cake recovered in step 2 is dried to obtain dry powder, the dry powder is heat-treated at 957 ° C. for 4 hours in a furnace in an air atmosphere, and substituted ε-oxidation coated with silicon oxide. A powder composed of iron particles was obtained.

(Procedure 4)
The powder of the substituted iron oxide particles coated with the silicon oxide obtained in step 3 is added to a 20 mass% NaOH aqueous solution and stirred at 60 ° C. for 24 hours to obtain the silicon oxide on the surface of the substituted iron oxide particles. A slurry containing substituted ε iron oxide particles was obtained by performing the removal treatment of.

(Procedure 5)
After centrifuging the slurry obtained in step 4 with a centrifuge, the supernatant liquid is removed, pure water is added to form a slurry, and the operation of centrifuging again with a centrifuge is repeated. The supernatant of the slurry obtained in No. 4 was washed until the conductivity was ≦ 15 mS / m.

(Procedure 6)
Next, a 25% by mass tetramethylammonium hydroxide (hereinafter referred to as TMAOH) aqueous solution as a surface modifier was added to the washed slurry obtained in step 5 to obtain a surface modifier-containing slurry. rice field. The amount of the TMAOH aqueous solution added was such that the TMAOH concentration in the slurry containing the surface modifier was 0.065 mol / kg.

(Procedure 7)
The surface modifier-containing slurry 40 g obtained in step 6 was subjected to ultrasonic dispersion treatment for 1 hour with an ultrasonic cleaner (Yamato5510 manufactured by Branson (Yamato Scientific Co., Ltd.)), and then subjected to the hydrothermal treatment described below. Performed the previous preliminary classification.

40 g of the surface modifier-containing slurry after the ultrasonic dispersion treatment is centrifuged at a rotation speed of 20000 rpm for 30 minutes using the R20A2 rotor of a centrifuge (Himac CR21GII, manufactured by Hitachi Koki Co., Ltd.), and the supernatant slurry is processed. 30 g was recovered. The gravitational acceleration in the centrifugation process was 48,000 G.
On the other hand, 30 g of a 0.065 mol / kg TMAOH aqueous solution was added to 10 g of the slurry on the precipitation side, and then ultrasonic dispersion was performed again. Then, again, centrifugation was performed at 20000 rpm and 48000 G for 30 minutes, and 30 g of the supernatant slurry was recovered. On the other hand, 30 g of a 0.065 mol / kg TMAOH aqueous solution was added again to 10 g of the slurry on the precipitation side. By repeating this operation 9 more times, a total of 300 g of the supernatant slurry was collected. After mixing the recovered 300 g of the supernatant slurry, 40 g of the supernatant slurry was separated from this.

Centrifuge 40 g of the separated supernatant slurry for 60 minutes at a rotation speed of 20000 rpm using the R20A2 rotor of a centrifuge (Himac CR21GII, manufactured by Hitachi Koki Co., Ltd.) to remove 30 g of the supernatant slurry containing fine particles. Then, 10 g of the slurry on the precipitation side was obtained. The gravitational acceleration in the centrifugation process was 48,000 G.
Then, 30 g of a 0.065 mol / kg TMAOH aqueous solution was added to 10 g of the slurry on the precipitation side, and then ultrasonic dispersion was performed again. Then, after centrifuging again at 20000 rpm and 48000 G for 60 minutes, 30 g of the supernatant slurry was removed to obtain 10 g of the slurry on the precipitation side. By repeating this operation 9 more times, 10 g of the precipitate-side slurry was obtained.

After adding 30 g of a 0.065 mol / kg TMAOH aqueous solution to 10 g of the obtained precipitate-side slurry, ultrasonic dispersion treatment was performed for 1 hour with an ultrasonic cleaner (Yamato5510 manufactured by Branson (Yamato Scientific Co., Ltd.)). rice field. After that, 40 g of the slurry on the settling side after the ultrasonic dispersion treatment was centrifuged at a rotation speed of 20000 rpm for 45 minutes using the R20A2 rotor of a centrifuge (Himac CR21GII manufactured by Hitachi Koki Co., Ltd.), and the supernatant slurry was performed. 30 g was removed to obtain 10 g of a slurry on the precipitation side. The gravitational acceleration in the centrifugation process was 48,000 G.
On the other hand, 30 g of a 0.065 mol / kg TMAOH aqueous solution was added to 10 g of the slurry on the precipitation side, and then ultrasonic dispersion was performed again. Then, again, centrifugation was performed at 20000 rpm and 48000 G for 45 minutes to remove 30 g of the supernatant slurry to obtain 10 g of the slurry on the precipitation side. By repeating this operation 9 more times, 10 g of the precipitate-side slurry was obtained.

To 10 g of the obtained precipitate-side slurry, 30 g of pure water was added and ultrasonically dispersed with an ultrasonic cleaner (Yamato5510 manufactured by Branson (Yamato Kagaku)) for 1 hour, and then a 1% by mass aqueous sulfuric acid solution was used. Was added to adjust the pH to 6.5. After centrifuging the precipitated slurry after adjusting the pH with a centrifuge, remove the supernatant liquid, add pure water to make a slurry, and repeat the operation of centrifuging again with a centrifuge to repeat the slurry. The supernatant was washed until the conductivity was ≦ 1 mS / m. Then, pure water and 20% by mass NaOH were added to the slurry to adjust the pH to 10, and a slurry containing substituted ε-iron oxide particles was obtained.

(Procedure 8)
A 1% by mass aqueous sulfuric acid solution was added to the slurry containing the substituted iron oxide particles obtained in step 7 to adjust the pH to 6.5, and after the substituted iron oxide particles were aggregated, a membrane filter ( The solid content was recovered by filtering with a pore size of 0.2 μm). The recovered solid content was dried to obtain an iron-based oxide magnetic powder. When the composition analysis of Fe and Ga was carried out on the obtained iron-based oxide magnetic powder, it was found that Fe: Ga = 1.92: 0.08 in terms of molar ratio. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 0%.
On the other hand, when TEM observation was performed on the slurry containing the substituted ε iron oxide particles obtained in step 7 and the particle diameters of 200 particles contained in the slurry were measured, the TEM average particle diameter was 10. The number ratio of particles having a particle size of 9.9 nm and a particle size of 8 nm or less was 7.8%, and the coefficient of variation (CV value) was 19%.

(Procedure 9)
Pure water and a 4% by mass NaOH aqueous solution are added to the slurry containing the substituted iron oxide particles obtained in step 7 so that the content of the substituted iron oxide particles is 2% by mass and the pH is 12. It was adjusted. Then, 4.5 mL of the adjusted slurry is placed in a 5 mL airtight container and subjected to hydrothermal treatment at a treatment temperature of 200 ° C., a treatment time of 5 minutes, and a pressure of 40 MPa to obtain a slurry of substituted ε-iron oxide particles according to Example 10. Obtained.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above.

(Procedure 10)
When TEM observation was performed on the slurry obtained in step 9 and the particle diameters of 200 particles contained in the slurry were measured, the TEM average particle diameter was 11.0 nm and the number of particles having a particle diameter of 8 nm or less. The ratio was 3.9% and the coefficient of variation (CV value) was 19%. FIG. 5 shows a TEM photograph of the substituted ε iron oxide particles according to Example 10.
The obtained slurry of the substituted iron oxide particles according to Example 10 was dried to obtain an iron-based oxide magnetic powder according to Example 10. FIG. 6 shows a TEM photograph of the iron-based oxide magnetic powder particles according to Example 10.
The obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 0%. The results of measuring the magnetic properties of the obtained iron-based oxide magnetic powder are shown in Table 2 together with the measurement results of the α phase content and the chemical composition.
Table 2 shows the measurement results of the substituted ε-iron oxide particles and the iron-based oxide magnetic powder described above.

[Example 11]
In step 9 of Example 10, pure water, a 4% by mass NaOH aqueous solution and ferric nitrate are added to the slurry containing the substituted ε-iron oxide particles obtained in Step 7 of Example 10, and the substituted ε-oxidation is performed. The content of iron particles was adjusted to 2% by mass, the pH was 12, and the Fe (III) ion concentration was 0.056 mol / kg. The slurry containing the substituted ε-iron oxide particles according to Example 11 and the implementation were carried out by the same procedure as in Example 10 except that the hydrothermal treatment was carried out using 2.2 mL of the prepared slurry for a treatment time of 10 minutes. An iron-based oxide magnetic powder composed of particles of substituted ε-iron oxide according to Example 11 was obtained.
As described in procedure 10 of Example 10, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Example 11, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 11.8 nm, the number ratio of particles having a particle diameter of 8 nm or less was 1.3%, and the coefficient of variation (CV value) was 15%. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 0%.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder. As for the chemical composition, the substituted ε-iron oxide particles contained in the slurry obtained in step 7 of Example 10 and the iron contained in the iron nitrate added to the slurry were all recovered as solids. It was calculated as a thing (hereinafter, the same applies to Example 12).

[Example 12]
In step 9 of Example 10, pure water, a 4% by mass NaOH aqueous solution and ferric nitrate are added to the slurry containing the substituted ε iron oxide particles obtained in Step 7 of Example 10 to oxidize the substituted ε. Adjust so that the iron particle content is 2% by mass, the pH is 12, and the Fe (III) ion concentration is 0.056 mol / kg, and then an ultrasonic homogenizer (device name: Branson (Yamato Scientific Co., Ltd.), Yamato 4500). After irradiating with ultrasonic waves for 120 minutes, the obtained slurry was subjected to hydrothermal treatment using 2.2 mL of the obtained slurry under the condition of a treatment time of 10 minutes, according to the same procedure as in Example 10 in Example 12. An iron-based oxide magnetic powder composed of the slurry containing the substituted iron oxide particles according to the above 12 and the particles of the substituted iron oxide according to Example 12 was obtained.
As described in step 10 of Example 10, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Example 12, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 12.0 nm, the number ratio of particles having a particle diameter of 8 nm or less was 0.4%, and the coefficient of variation (CV value) was 14%. Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 0%.
Table 1 shows the treatment conditions and the hydroheat treatment conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder.

[Comparative Example 2]
Comparative Example according to the same procedure as in Example 10 except that the slurry containing the substituted ε-iron oxide particles obtained in the procedure 7 of the example 10 was not subjected to hydrothermal treatment in the procedure 9 of the example 10. An iron-based oxide magnetic powder composed of a slurry containing substituted ε-iron oxide particles according to No. 2 and particles of substituted ε-iron oxide according to Comparative Example 2 was obtained.
As described in the procedure 10 of Example 10, TEM observation was performed on the obtained slurry containing the substituted ε-iron oxide particles according to Comparative Example 2, and the particles of 200 particles contained in the slurry were observed. When the diameter was measured, the TEM average particle diameter was 10.9 nm, the number ratio of particles having a particle diameter of 8 nm or less was 7.8%, and the coefficient of variation (CV value) was 19%.
Further, the obtained iron-based oxide magnetic powder was subjected to XRD measurement, and the α phase content was determined to be 0%.
Table 1 shows the processing conditions for the raw material slurry described above. Table 2 shows the measurement results of the substituted ε iron oxide particles and the iron-based oxide magnetic powder.

[Comparative Example 3]
This is an experimental example in which a slurry containing iron hydroxide was used as the raw material slurry instead of the slurry containing substituted ε-iron oxide particles.
4.455 mL of a liquid adjusted to pH 12 by adding a 4 mass% NaOH aqueous solution to a ferric nitrate (III) nitrate aqueous solution (Fe (III) ion concentration 0.055 mol / L) was placed in a 5 mL closed container, and the treatment temperature was 200 ° C. A slurry containing the iron oxide particles according to Comparative Example 3 was obtained by performing an aqueous heat treatment at a pressure of 40 MPa for a treatment time of 10 minutes.
The obtained slurry containing the iron oxide particles according to Comparative Example 3 was washed and dried after solid-liquid separation to obtain the iron oxide powder according to Comparative Example 3. As a result of XRD measurement of the obtained iron oxide powder, it was confirmed that the _{obtained iron oxide powder had a crystal structure of α-Fe 2} O _{3 and α-Fe OOH.}
The hydrothermal treatment conditions described above are shown in Table 1. Table 2 shows the measurement results of iron hydroxide particles and iron-based oxide powder.

Claims (11)

A raw material slurry containing particles of ε-iron oxide in which a part of Fe sites is substituted with other metal elements is subjected to hydrothermal treatment, and ε-oxidation in which a part of Fe sites is substituted with other metal elements. A method for producing an iron-based oxide magnetic powder composed of iron particles. The hydrothermal treatment reduces the number ratio of particles of ε-iron oxide in which a part of the Fe site is replaced with another metal element and whose particle size is 8 nm or less as measured by a transmission electron microscope. The method for producing iron-based oxide magnetic powder according to claim 1. The method for producing an iron-based oxide magnetic powder according to claim 2, wherein the ratio of the number of particles having a particle diameter of 8 nm or less measured by the transmission electron microscope is reduced to 4% or less. The method for producing an iron-based oxide magnetic powder according to any one of claims 1 to 3, wherein the hydrothermal treatment is performed at a temperature of 120 ° C. or higher. The method for producing an iron-based oxide magnetic powder according to any one of claims 1 to 4, wherein the hydrothermal treatment is performed at a pressure of 0.2 MPa or more. The method for producing an iron-based oxide magnetic powder according to any one of claims 1 to 5, wherein the raw material slurry containing the particles of ε-iron oxide has a pH of 6 or more and 14 or less. The raw material slurry containing the ε-iron oxide particles contains ε-iron oxide particles having an average particle diameter of 10 nm or more and 20 nm or less as measured by a transmission electron microscope, in which a part of Fe sites is replaced with other metal elements. The method for producing an iron-based oxide magnetic powder according to any one of claims 1 to 6, wherein a slurry is used. The method for producing an iron-based oxide magnetic powder according to any one of claims 1 to 7, wherein Ga is used as another metal element that replaces a part of the Fe site. The iron-based oxidation according to any one of claims 1 to 8, wherein the raw material slurry containing the particles of ε-iron oxide is subjected to hydrothermal treatment after being irradiated with ultrasonic waves and / or added with metal ions. Method for manufacturing magnetic powder. The average particle size measured by a transmission electron microscope is 10 nm or more and 20 nm or less, the number ratio of particles having a particle size of 8 nm or less is 4% or less, and the α-type iron oxide measured by the X-ray diffractometry. An iron-based oxide magnetic powder composed of ε-iron oxide particles in which a part of Fe sites is replaced with another metal element, which is characterized by a content of 10% or less. The iron-based oxide magnetic powder according to claim 10, wherein the other metal element that replaces a part of the Fe site is Ga.

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